Photometer



C. W. DAKE June 24, 1930.=

PHOTOMETER Filed Jan. 3, 1928 2 Sheets-Shet 1 INVENTOR Carze s BYATTORNEYS- June 24, 1930. c. w. DAKE 1,766,219

PHOTOMETER Filed Jan. 5, 1928 2 Sheets-Sheet 2 INVENTOR Patented June24, 1930 v UNITED STATES PATENT pm E mums w. mum, on CHICAGO, ILLINoIs,essIeNoa To an rYLaNA'rIoN'AL com. PANY, or CHICAGO, ILLINOIS, ACORPORAT ON or NEW JERSEY rnocromn'rnn Application filedl'anuary 3,1925. Serial No. 244,100.

My invention relates to improvements in photometers and has for oneobject to provide a new and improved form of portable photometer whereinthe determination of light intensity, either in terms of beam candlepower or foot candle power as the case .may be, is made by comparisonwith darkness rather than light, by the use of an adjustable shutter ofprogressive degrees of opacit My invention is especially adapte for usein connection with the determination of candle power of locomotiveelectric head lights and the like, might be used with equal conveniencein many other circumstances.

My invention is illustrated more or less diagrammatically in theaccompanying drawings, wherein- I Figure 1 is a p an view;

Figure 2, a section along the line 2-2 of Figure 1;

Figure 3, a section along the line 3--3 of Fig. 1;

Figure-4, a side elevation;

Figure 5, a plan view of the variable element;

Figure 6, a plan view of the bottom floor of the housing of theapparatus.

A is the floor or bottom plate. It is provided with a lug A adapted tointerlock with the cylindrical wall A of the'housingA to form. a flat,cylindrical receptacle, the inside of which is coatedwitlrlight-absorbing material. The interlocking ofthe lug A with thewall A centers the bottom floor A in position. This' is important,because on it is mounted a reflector A. This reflector may bean'incline'd mirror or a prism, as the case may be, but in either caseis rigidly and permanently positioned on the floor A and is surroundedby a housing open at the top and providedwith a small aperture A throughwhich light rays coming in from the top may be reflected outwardlyacross the axis of the cylindrical housing.

In that part of the cylindrical wall A in line with the opening A is asleeve B, in which is slidably mounted an adjustable tube B having aneye-piece B apertured at B The bottom of the tube is closed by a wall Bbut it is obvious that it' apertured at B, the apertures B B and A beingall in line and serving merely to prevent anything except the light raysdirectly reflected from thereflector or mirror reach; ing the eye of theobserver when he places it. against thecup.

-The cover A is apertured immediately above the reflector. In thisaperture is threaded a cup C closed at C butthe closure being aperturedat C G is a glass closing 50 the cup and overlying the aperture, 0 apacking ring engaging the glass and associated with the band C to lockthe glass in place and make a dusttight closure for the receptacle. C ispacking carried by the bot- .55

tom'of'the cup to prevent light entering laterally into the housing.-

' D is a supporting wheel having'a threaded shank D engaging in threadedrelation the hub D The hub D carries a knarled adj ustmg hand wheel Dand the parts are arranged, when shown in position as in Fig. 2, sothatthe hub D makes a tight bearing with the aperture in the cover so as topermit rotation ofhub and wheel, Mounted on the-support- 7} ing wheel Dis the circular shutter D, which may be made of glass, celluloid, or anyother suitable material. Arranged intermediate the outer periphery ofthis shutter and its center of rotation is a light interfering band D,made of varying degrees of opacity from zero opacity to 100 per cent.The parts are so arranged that this band'lies beneath the aperture 0 andall light entering through that aperture, to reach the reflector, mustpass through it. The packing above referred to around the cup C insuresthat there will be no reflected light leaking into the photometerhousing without passing through the interfering shutter, Arranged aboutthe outer periphery of the shutter D, and in register withthe varyingdegree'intensity of the shutter, is a numerical scale which may becalibrated on any desired basis, either arbitrary "orunot, as the casemay be, but which scale State of Illinois, this 28th day of December,

ture and E a frame wherebyithis window may be locked in place.

The use and operation of my invention are as follows:

The operator first draws out the slide to its full extension, thenpoints the top of the photometer toward the light which he wishes tomeasure. The light passing in throu h the aperture inthe top travelsthrough t e'variable "shutter, reaches and is reflected .from thereflecting surface through the three apertures in three parallel wallsto the e e of the observer The small openings cut own the exposedsurface and neutralize all difierences in eye-sight, so that an one whocan see at all can make the determination.

Since the interior of the housing is dead black, since only a very thinpencil of light passes to or is reflected from the housing, and

since the li ht that the observer sees is the small roun hole in themiddle of the wall between him and the reflector, all he sees is a rounddisk of bright light incontrast with the dead black background. If theoperator 7 then rotates the hand-Wheel on the outside of thehousing,bringing an increasingly opaque part ofv the shutter into linewith the opening leading to the reflector, he will finally reach a pointwhere all light is shut OE and where he can not see any light in thephotometer at all. This can be checked .by rotating '.the hand-wheel inthe opposite direction until light is seen and then returning it. untilthe light disappears. Experience shows that a number of observations ofthis kind with the opaque shutter set to just completely cut 011' lightresults in giving a very accurate determination of the beam or footcandle power. v

I claim A photometer comprising a flat cylindrical housing, one of thecurved walls being apertured, a tubular socket located within saidaperture and extending into the housing, an eye piece tube thereon, areflector in line with the axis of the eye piece, a wall projectingupwardly from the base of the reflector, a plurality of walls associatedwith the reflector being apertured in line, a light opening in one ofthe fiat walls of the housing in register with the reflector, a shuttermounted on the flat wall of the housing of varying opacity and a handwheel projectin through the wall whereby this shutter may he adjustedtomask with progressive degrees of opac- I ity the light opening,a'reading scale on the shutter, the wall of the reflector beingapertured in register with said scale to ermit determination of theshutter position y the use of said scale.

V Signed at Chicago county of Cook and CHARLES W. DAKE.

